1. Field of the Invention
Embodiments provided herein generally relate to reflectivity metrology. More specifically, embodiments provided herein relate to a test apparatus for reflective cavity characterization.
2. Description of the Related Art
Thermal processing is commonly practiced in the semiconductor industry. Semiconductor substrates are subjected to thermal processing in the context of many transformations, including doping, activation, and annealing of gate, source, drain, and channel structures, siliciding, crystallization, oxidation, and the like. Techniques of thermal processing have progressed from simple furnace baking to various forms of increasingly rapid thermal processing such as spike annealing and laser annealing.
Rapid Thermal Processing (RTP) is a well-developed technology for fabricating semiconductor integrated circuits. RTP is a process in which the substrate is irradiated with high intensity optical radiation in an RTP chamber to quickly heat the substrate to a relatively high temperature to thermally activate a process in the substrate. Once the substrate has been thermally processed, the radiant energy is removed and the substrate cools. RTP is an energy efficient process because the chamber in which the RTP is performed is not heated to elevated temperature required to process the substrate. In an RTP process, only the substrate is heated. Thus, the processed substrate is not in thermal equilibrium with the surrounding environment, namely the chamber.
Although annealing in early stages substrate processing technology involved heating multiple substrate for long periods in an annealing oven, RTP has been increasingly used to satisfy ever more stringent requirements for processing substrates with increasingly smaller circuit features. RTP is typically performed in a single substrate chamber by irradiating a substrate with light from an array of high intensity lamps directed at the substrate. The radiation is at least partially absorbed by the substrate and quickly heats the substrate to a desired high temperature. The desired temperatures generally are above 600° C. and in certain applications, above 1000° C. The radiant heating can be quickly activated and deactivated to controllably heat the substrate over short time intervals, such as between about 60 seconds and about 1 second.
An array of high intensity lamps providing heat to the substrate may be designed in various manners to irradiate the substrate. Some arrays utilize reflective cavities having an electromagnetic radiation source disposed therein. The reflective cavities generally affect how the electromagnetic radiation is provided to the substrate, such as the total amount of light as well as the spatial and frequency distribution of the light. Thus, it is generally desirable to be able to measure the reflectivity of the reflective cavities. Integrating spheres are generally used to measure various spatially integrated qualities of electromagnetic radiation. While integrating spheres provide a convenient way to measure the total light released from a lamp reflector system, the measurement combines attributes of the lamp with those of the reflector. Moreover, many integrating spheres lack the capability of measuring reflectivity from a reflective cavity. Thus, what is needed in the art is an apparatus for measuring reflectivity of reflective cavities, such as reflective cavities for an array of high intensity lamps for use in an RTP process.